Polyamide-polyether block copolymers have been employed previously as durable antistatic additives for polyamides, but the copolymers have been limited to the linear, aliphatic and the branched, aliphatic types. For example, in U.S. Patent 3,549,724, polyamide-polyether antistatic additives utilizing polymers of a similar structure using branched chain polyamides are described. U.S. Pat. No. 3,839,245 describes poly(ether-esteramide) copolymers derived from dimer acids, which are used commercially as antistatic additives to nylon. Ethoxylated hydantoin compounds which have been described in U.S. Pat. No. 3,928,298 for use as antistatic additives have the disadvantage that they are not thermally stable.
A useful antistatic additive for polyamides must withstand the stringent conditions of polyamide processing (mainly high temperature) and must be nontoxic and chemically inert. It should have an affinity for moisture, but should not be water soluble. In addition, it must be lightfast, heatfast, and resistant to gas fading. Also it must not adversely affect fiber properties, a factor which is best approached by requiring the additive be a separate phase in polyamides. The most important property of the additive, however, is that it is capable of imparting antistatic characteristics to the fiber itself, and this is primarily dependent upon the additive's resistivity, dispersibility, and shapeability within the fiber.
Dispersibility and shapeability may be considered a function of the rheological properties and the compatibility of the additive with respect to polyamides, such as nylon 6; the polyamide block of the polyamide-polyether antistatic additives is best suited for maximizing these properties. Linear aliphatic and branched aliphatic polyamides are the only types that are known to have been used for this purpose to date. Both types are hydrophobic in nature. Consequently, the polyamide blocks of these antistats do not contribute to the antistatic propensity of the additive (other than causing the copolymer to be amorphous), primarily due to the low affinity of polyamides for moisture.